A mechanical seal that seals a gap between a rotating shaft and a housing thereof is to be manufactured according to Generals Rules of JIS-B2405. The mechanical seal includes a rotating ring which is air-tightly attached to a sleeve fitted to an outer circumference of the rotating shaft so as to rotate therewith, and rotates with the sleeve, and a fixed ring which is air-tightly attached to a seal cover fixed to the housing, and does not rotate. The rotating ring and the fixed ring are disposed in sliding-contact with each other at a sliding interface oriented perpendicular to the shaft, and constitute a seal ring in which one is a mating ring immovably disposed in an axial direction and the other is movable in an axial direction and biased by a spring so as to be pressed against the mating ring.
In the mechanical seal, a sealing fluid such as a lubricant provided on the sliding interface completely seals the gap of the sliding interface. An increase in temperature of the sliding interface because of the friction between the rotating ring and the fixed ring may cause deterioration of the sealing fluid, or may provoke denaturation of impurity such as a process gas dissolved in the sealing fluid, thereby leading to generation of a solid degradation material. Such degradation material incurs a damage called “blistering” on the sliding interface, once stuck thereon. The degradation material falsely extends the sliding interface thus to form a secondary sliding interface when stuck to a peripheral region of the sliding interface, which reduces the contact pressure between the rotating ring and the fixed ring, thereby resulting in degraded sealing performance of the mechanical seal.
To prevent the generation of the degradation material, it is effective to reduce the contact pressure or the sliding-contact area between the rotating ring and the fixed ring to thereby reduce the heat generation, however this incurs a disadvantage that the sealing performance is degraded.
Alternatively, as disclosed in JP-A2004-293765, a flow path called “hydro-cut portion” for the sealing fluid may be provided for efficiently cooling the rotating ring and the fixed ring with the sealing fluid. This method, however, leads to increased leak of the sealing fluid to a region where the pressure is lower.
Also, JP-A2003-74712 discloses a mechanical seal that forcibly provides a quenching fluid such as steam around the sliding interface for cooling of the sliding interface. Providing the quenching fluid, however, requires an additional equipment, which inevitably leads to an increase in cost.
In view of the foregoing situation, an object of the present invention is to provide a mechanical seal that prevents deposition of a degradation material generated on a sliding interface.